I didn't know to be honest, I'd just assumed it would be 0.64, because <"that is the normal conversion factor for fresh water">.As far as I am aware, none of Hannas TDS devices uses 0.64 ... only 0.5 (low range TDS) or 0.7 (higher range TDS).
Neither did I until I started to look into it a while ago. I suppose the TDS 442 standard (40% Na2SO4, 40% NaHCO3, 20% NaCl) that has been used for ages as a "natural fresh water standard" may not be as good a standard as the more stable KCl solution that is now the international standard for calibration of instruments used for conductivity measurements.Hi all,
I didn't know to be honest, I'd just assumed it would be 0.64, because <"that is the normal conversion factor for fresh water">.
I've always used potassium chloride (KCl) for the <"calibration standards">. The secret is to make up a large volume <"fairly accurately"> and then only use each aliquot once. We will have some "442" calibration standard somewhere, but I've always made the calibration standards for the conductivity meters.more stable KCl solution that is now the international standard for calibration of instruments used for conductivity measurements.
Hi @hypnogogiaI wonder if @jaypeecee also has a view?I seem to remember him mentioning tds meters as well.
I got a cheap China one but it actually works well. It costs so little, you can try it out (the experience I have had generally with this sort of stuff is that when you get a good sample, it actually is pretty good, its just that the QC is inconsistent)
If I test pure RO water, my meter reads 0ppm. Using my limited amount of maths/chem knowledge, I add Epsom Salt and/or Calcium Chloride to the RO water to achieve various ppm levels and the TDS meter is roughly +/- a few percentage points of the theoretical levels. So I would say, good enough for a tenner. For serious chemistry, obviously a few percentage points is unacceptable, but for aquarium use, I'm ok with it.
This is the one I use and it is very good, it has temperature compensation which makes it very accurate.
I have tested it with a calibration standard but wouldn't again, it is fine for my needs and saved me £40Ok, here is a way to figure out if you saved 40 quid or wasted a tenner:
You will need a microgram scale, pure NaCl and 1 liter of distilled water (at room temperature say 21C).
1. carefully measure and add 0.1 gram of NaCl to 1 liter of distilled water at room temperature - stir it carefully and let the water settle. Measure and write down the TDS
2. Repeat step 1 three more times.
You should measure 100, 200, 300 and 400 ppm depending on your meters internal conversion factor.
Now, more importantly, If you can draw a reasonable straight line between these 4 points then you're all good regardless of your brand, make or model of your TDS meter. If not, get a replacement
Yes, me too. Unfortunately, not much in this hobby refers to uS/cm.
Generally true, but not this this chart in particular. If your referring to the depicted curve, keep in mind that everything that is important to us in this hobby is in the 0-1000 uS/cm range - which is an indiscernible fraction of the beginning of this curve...You may also find the following chart useful. Can't beat a picture!
No we don't. I have been a happy aquarium keeper for decades without owning a TDS meter for sure, but if your deeper into the water chemistry bit, I merely suggest to make sure your measurement device(s) are honest with you - if you can find them cheaply thats just perfect. If you mix RO water and the quantities of carefully measured compounds you add to the water checks out with your TDS then you're very likely good to goDo we really need really expensive meters for general fish tank usage?
Hi @MichaelJGenerally true, but not this this chart in particular. If your referring to the depicted curve, keep in mind that everything that is important to us in this hobby is in the 0-1000 uS/cm range - which is an indiscernible fraction of the beginning of this curve...